Simple pricing. Really nice management features. No need to hunt for promos or stuff to get cheap domains... a bit friendlier than GoDaddy.
I've never done a price comparison so I can't say for certain that Namecheap is the cheapest, but I can vouch that they are one of the most reliable sites to purchase a domain from. It's the only place I buy my domains from.
I only purchase domains from Namecheap. Simple pricing and no BS. Extremely reliable and most importantly has better security features than it's competitors (two factor Auth for any changes on your domains). Updates like NS servers are virtually instaneous. Also I like that thier WHOIS Guard (domain protection) is included for the first year of a domain and is only $2 a year after that. Lastly thier domain prices don't fluctuate (like how godaddy charges you more after the first year). My only complaint is that when searching for a domain, they try to push random TLDs like .fyi and .wtf and stuff before .com and .net. Just add the tld you want in the search bar to avoid this (domain.com instead of domain) and then it will pull the .com to the top. I don't shop price, I host all domains in Namecheap. You can find 99¢ and $2 domains from other providers for the first year but most those providers jack the price up to $15-$20 a year after that. Namecheap is always $9.80 a year for a .com. That's fair to me and I like everything else they provide that I don't buy domains anywhere else.
I use Hover to purchase TLD's. They offer better pricing than namecheap + godaddy for TLD's.
Hover has been my go-to for the past year. With all registrars mostly accomplishing the same thing. I think it really comes down to UI and management tools. I've found hovers to be some of the easiest to use. Interface is clean / they don't spam you. Seems like a good/honest company in general.
They have an amazing dashboard and free private whois. Also, Google
One of the most popular products - they usually have coupon codes for .coms if it's your first account. Can't say anything about their uptime or reliability.
Gandi.net - "No Bullshit" Gandi.net's not the cheapest, but the quality of their products/services make it well worth the extra money. Why's Gandi.net great? - Free Private Domain Registrations (~$5-$7/year typically) - Customer Service is second to none - They donate to the Electronic Frontier Foundation, which fights to protect our free speech rights. - They oppose the SOPA legislation - They won't SPAM you https://v4.gandi.net/no-bullshit